Method and apparatus for determining the thickness and index of refraction of a film using low coherence reflectometry and a reference surfaces

An apparatus for measuring the thicknesses of the layers of a multilayer transparent film having top and bottom surfaces, said apparatus comprising:

• means for generating a probe light signal from a low coherence light source and applying said probe light signal to said film;
• a partial reflector positioned on one side of said film such that said reflector reflects a portion of said probe light signal;
• means for collecting light reflected by said reflector and said film;
• and
• a receiver for receiving said collected light signal and for determining the time delay between light reflected from said top and bottom surfaces and one or more internal layer interfaces of said film and said reflector.

A method for measuring the thickness and group index of refraction of a transparent film having top and bottom surfaces, said method comprising the steps of:

• generating a probe light signal from a low coherence light source and applying said probe light signal to said film;
• providing a first reflector, said first reflector being partially transparent;
• providing a second reflector, said film being positioned between said first and second reflectors, said probe light signal being applied to said film after passing through said first reflector, said second reflector reflecting the portion of said probe light signal leaving said film back toward said first reflector;
• collecting light reflected back toward said first reflector;
• and
• determining the time delay between light reflected from said top and bottom surfaces of said film from said collected light and for determining the change in optical path between said first and second reflectors when said film is placed between said first and second reflectors in a receiver, said thickness and group index being determined from said time delay and said change in optical path.

A method for measuring the thicknesses of the layers of a multilayer transparent film having top and bottom surfaces and one or more internal layer interfaces, said method comprising the steps of:

• generating a probe light signal from a low coherence light source and applying said probe light signal to said film;
• providing a reflector to reflect a portion of said probe light signal;
• collecting light reflected by said film and said reflector;
• and
• determining the time delay between light reflected from said top and bottom surfaces and said internal layer interfaces of said film and said reflector from said collected light.